The ability of 2-haloethyl phosphonic acid compounds to regulate plant growth is well known and is described for example in U.S. Pat. Nos. 3,879,188; 4,144,046, 4,240,819; 4,352,689: 4,374,661; and 4,401,454. These phosphonic acid plant growth regulators, when applied to plants, elicit a variety of different responses, such as increased yields, faster and more uniform ripening of fruit, induction of antilodging effects, breaking of apical dominance and the like, collectively referred to as ethylene or ethylene-type responses.
The preferred and most widely used phosphoric acid plant growth regulator compound is 2-chloroethylphosphonic acid which is known by the generic name "ethephon". Ethephon is normally stored in solution of relatively high concentration for reasons of convenience and to minimize degradation which begins to occur at pH levels above about pH 5. In concentrated form ethephon exhibits a pH of about 1.0. The concentrated solution is customarily diluted prior to application to plants at concentrations which exhibit a pH of about 3.5.
The most commonly used solutions of ethephon for plant treatment are aqueous solutions which are applied by conventional spray equipment. However, newer methods of application such as ultra-low volume (ULV) spray apparatus, work more effectively with non-aqueous solutions of the active chemical with oil based formulations being most preferred. Oil-based formulations of ethephon have the added advantage of better penetration of plant tissue than aqueous formulations.
A particular problem which it is sought to overcome by this invention is the rapid evaporation of water from aqueous formulations of ethephon which sometimes occurs when aqueous formulations of ethephon are applied through ULV apparatus. Such evaporation is so rapid that in some instances only the dry active reaches the plant.
The preparation of an oil-based formulation of such phosphonic acid plant growth regulators is therfore desirable both for improved plant tissue penetration and to permit application of these plant growth regulators with ULV apparatus. However, formulation of the phosphonic acid directly in an oil diluent is disfavored since the production of such formulations requires the use of essentially anhydrous phosphonic acid plant growth regulator. These strongly acidic phosphonic acid compounds are extremely hygroscopic and hence the anhydrous product is difficult and costly to prepare and difficult to maintain.
Formulations of aqueous solutions of agricultural chemicals in an oil base are known in the art. Preparation of these emulsions or dispersions is accomplished by mixing the desired oil, water, active ingredient and an emulsifier in appropriate amounts to achieve the desired formulation. Such emulsion compositions are typically 30-80% by weight oil and 10-40% water. The emulsifier is present in smaller amounts, seldom exceeding 15% by weight of the final composition and more often at concentrations of 4-10%.
The preparation of chemically stable oil emulsions of the phosphonic acid growth regulators has proven difficult due to the low pH exhibited by these compounds. This low pH encourages the degradation of emulsifiers which rapidly erodes the stability of the emulsion and leads to phase separation. This severely limits the utility of these emulsions as spray formulations since phase separation of the spray formulation results in poor dispersion of phosphonic acid plant growth regulator in the target area.
Separation of formulation components may also cause the formation of solids which could clog the spray equipment. Acidic elements of the formulation, which are safe when dispersed in the oil carrier, can also cause rapid corrosion of spray equipment if the phases separate.